This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Pine and oak woodlands are some of the most widespread floral communities in North America. They are distributed across the continent at mid-latitudes, but do exist as far north as British Columbia and as far south as Nicaragua. They are also disjunct habitats with distinct regional species. The division of pine-oak forests into specific regional communities should be mirrored by patterns of faunal diversity. However, there are a number of bird species that exhibit widespread distributions across the disjunct pine-oak communities. The evolution of the widespread distributions exhibited by these birds can be explained by three alternative historical hypotheses. (1) The species evolved in situ in the regional pine-oak communities and the isolation of populations in these regions is captured in cryptic genetic variation. (2) Migration of individuals between regions has been frequent enough to maintain the widespread distributions and prevent regional divergence. (3) The species have recently expanded to occupy their current distributions. I explore which of these historical hypotheses best explains the widespread distributions of the Pygmy Nuthatch (Sitta pygmaea), Mountain Chickadee (Poecile gambeli), and White-breasted Nuthatch (Sitta carolinensis) through a comparative phylogeographic study of mitochondrial DNA (mtDNA) variation in each of these species.